A hydraulic turbine according to the prior art generally comprises a shaft of approximately 1 m in diameter and a bearing assembly immersed in oil to support the rotating shaft. In particular, to absorb the radial forces exerted by the shaft, a plurality of bearing units are distributed about the axis of rotation. The bearing units generally comprise a stationary base, a resilient member and a bearing surface defining, together with the shaft, an oil film approximately 0.5 mm thick.
The function of the bearing units and the oil film is that of limiting bumping of the shaft on the bearing surfaces. This bumping is particularly caused by assembly defects of relatively moving parts and geometric defects due to manufacturing tolerances of relatively moving parts. In the standard case whereby the shaft has a diameter of approximately 1 m and the oil film is approximately 0.5 mm thick, the bearing assembly adapts well to assembly defects and geometric defects which are relatively minor.
However, such a bearing assembly according to the prior art is not suitable for effectively limiting marine turbine shaft bumping. Indeed, the compressibility of the oil gives rise to inertia liable to slow down the reactions of the bearing assembly. However, the large diameter of a marine turbine shaft gives rise to relatively significant and numerous assembly defects and geometric defects, requiring a bearing assembly reacting very rapidly to shaft oscillations. Moreover, immersing a marine turbine bearing assembly in oil gives rise to a pollution risk for the environment in which the marine turbine is placed.